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Topic: About reusable LM (Read 7275 times)

In case of reusable lunar module,how is possible do maintenance of this vehicle in space?Reusables vehicles must be reviewed between a a flight and the other; you not can simply putting fuel and starting.Generally maintenance of reusable space vehicles is very complex,and requires a specialized staff...How you can make this in lunar orbit in a little orbital outpost,with the LM supposedly docked outside in the vacuum of the space?

If ITS, New Armstrong or some equivalent happens, you might not need to service it in space. If the lander could be made to fit in a reusable vehicle's cargo area, you could cycle it back to Earth for maintenance.

Maintenance of a reusable LM is going to be very difficult in zero g in spacesuits; unless it were designed from scratch to be serviceable and upgradable, as the Hubble telescope was - but that is not an apples-to-apples comparison. But when we are dealing with a 'reusable' LM in the near-ish future; it will be a first generation 'Version 1.0' reusable LM, with all those inherent challenges and difficulties. It's likely one of three scenarios will occur:

1: Reusable LM's will be kicked down the road for a long time - put in the too-hard basket - in favor of a lightweight, cheap as possible expendable vehicle that can get small crews or modest cargo down to the Moon. It would likely use storable, hypergolic propulsion.

2: If the new LM is single-stage reusable craft (my preference), it will likely have ton-toxic RCS systems and propulsion. Propellants will (likely) be LOX/CH4, LOX/Kerosene, or LOX/Propane. The Main Descent/Ascent Engine set could be a removable module that can be replaced with another engine module brought occasionally from Earth when the engine develops flaws or wears out. Spacewalking Astronauts could install the module and hook it up to the propellant tank plumbing. I should think that the propellant tanks could be unbolted and replaced in a similar manner. The pressure cabin could have modular, replaceable life support systems and the main flight avionics can be designed to be replaced as complete electronic 'boxes'. Modularity; always...

3: Two-stage, partially reusable. In some ways, this would be the easiest design. How? Well, the Descent stage could be an expendable, hypergolically fueled module designed for one-way descent use. But we could get a bit cunning with it: It's doesn't have to be a 'deadweight' bit of hardware after descent. If the stage could have one or two retractable solar array sets mounted on it, once the Ascent Stage leaves, the solar arrays could be deployed to provide power for a small Outpost - just plug in a heavy-duty extension cable and enjoy a couple kilowatts of power. During an Outpost buildup, if the Outpost was surrounded by a few descent stages, instead of a solar array set, perhaps a couple of those Descent Stages could have a metric ton or so of RTG power units mounted aboard to give long Lunar night power supplies.

The Ascent Stage: A reusable craft that is designed for 5 or 10 (whatever) reuses. It is mated with a fresh Descent Stage brought from Earth with each new arriving crew. The Ascent Stage could also have a modular, replaceable Ascent engine module - or at least a replaceable nozzle extension for each time that nozzle erodes past usefulness. I would recommend that the RCS and main propulsion be LOX/CH4, LOX/Propane or LOX/Kerosene. Propellant supplies to fill the Ascent stage could be brought from Earth by Commercial suppliers or as a 'Tanker Module' brought with Orion Astronauts for each landing mission.

For the second and third options, we can assume that the reusable lander is operating out of a Lunar Orbital station or Depot staging point. For the expendable option, a Lunar space station is not strictly needed. Such a vehicle depending on the exact configuration and propulsion design, could mass anywhere between 25 and more than 30 metric tons.

« Last Edit: 07/13/2017 11:16 PM by MATTBLAK »

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{snip}For the second and third options, we can assume that the reusable lander is operating out of a Lunar Orbital station or Depot staging point. For the expendable option, a Lunar space station is not strictly needed. Such a vehicle depending on the exact configuration and propulsion design, could mass anywhere between 25 and more than 30 metric tons.

Anything that stays in orbit for more than 6 months and is visited at least twice is a space station. Propellant depot, staging post, repair hanger or full function are just the type of spacestation.

A lunar lander operates in a MUCH less stressful regime than a launch vehicle. Theres no reentry forces whatsoever. The engines produce orders of magnitude less thrust and usually burn for less time per mission. G forces are lower. Pressure differential is constant throughout the flight. Etc. If you can make a rocket that can reliably last 1 earth-launch mission before needing refurbishment (ie, the bare minimum for a reusable vehicle), and magically put that rocket on the moon, it should last several flights before receiving the same level of damage.

The Centennial Challenger 'Lunar Landers' required to be able to take off again within a hour. Masten's entry Xombie has had 227 flights. Their records may show the sort of servicing landers will need.http://masten.aero/vehicles-2/xombie

NASA's Project Morpheus lander was also reusable. There may be some very interesting information in its repair logs.

I see 4 categories of repairs and replacements:

a. Consumables, like propellant, food and air. Replaced every trip.

b. Mechanical consumables, items that need replacing every 2 or 3 flights. If they cannot be made to last a long time require them to be easy to change. I suspect that the heat protection on the feet may fit this category along with spark plugs.

c. Normal, things like engines that last several flights. They may have to be specified to be reused 10 or 50 times. Space walks and robots may be needed to repair or replace them.

d. Unfixable, one or more of these break - possibly in a crash - and the lander is scrapped.

If ITS, New Armstrong or some equivalent happens, you might not need to service it in space. If the lander could be made to fit in a reusable vehicle's cargo area, you could cycle it back to Earth for maintenance.

Errr, if ITS is possible, then why would you need a separate lunar lander? ITS would be the reusable, refuellable lunar lander.

If ITS, New Armstrong or some equivalent happens, you might not need to service it in space. If the lander could be made to fit in a reusable vehicle's cargo area, you could cycle it back to Earth for maintenance.

Errr, if ITS is possible, then why would you need a separate lunar lander? ITS would be the reusable, refuellable lunar lander.

I thought about that too, since it has been demonstrated on this forum in multiple threads that ITS could do a landing and return from the Moon using tankers. Ultimately, it comes down to effeciancy versus use; How many times will it be used, and how?

It would require R&D and useage of this vehicle to cost less than just using ITS and tankers. I think areas where a small dedicated lander could shine are tip-of-the-spear sortie type missions, areas an ITS couldn't practically go, or even to setup a landing pad for an ITS.

But there is no guarantee the economics work out. Using an entire ITS is less efficient, but might prove cheaper if launch costs get low enough. It's still too early to tell, imho, so I like seeing multiple approaches being considered.

You could build the vehicle with modular assemblies locked into a frame-like chassis, sort of like boards in a computer case. The assemblies would be designed as much as is possible to fit through a standard docking hatch.

If a thruster malfunctioned, then you'd remove the thruster assembly and swap in a spare. The faulty assembly could then be returned to Earth for repair. As most of the parts would be designed to fit through hatches used on spacecraft, it might be eventually possible to set up a repair module on either the ISS or a lunar base so that the more simple repairs could be done on site without cycling parts through Earth's gravity well.

If you designed it with expansion in mind, it might even be possible to link different assemblies together or even vehicles to provide more processing power or thrust for bigger jobs without having to design and test a new vehicle.

If a thruster malfunctioned, then you'd remove the thruster assembly and swap in a spare. T

so what is a "thruster assembly"? A nozzle with a thrust chamber? Does it include the cat bed (assuming it is mono prop). Does include the valve? Valve driver electronics? How much of the tubing? How many plumbing connections does it have? Or does it include the propellant tank itself and what about the pressurant? Is it safe to bring inside or are there flammability, high pressures or toxicity issues?

No, because we can't even do that type of diagnostic test on earth with complex metallic systems.

What about "non-complex"? My specific concerns are the propellant lines from powerhead to combustion chambers on the OME and main engine, as well as fatigue in the metal and/or composite structural beams (there's vibration and torsional stress). Is inspecting worth the hassle, of just estimate lifecycle and scrap when approaching it.

You could build the vehicle with modular assemblies locked into a frame-like chassis, sort of like boards in a computer case. The assemblies would be designed as much as is possible to fit through a standard docking hatch.

If a thruster malfunctioned, then you'd remove the thruster assembly and swap in a spare. The faulty assembly could then be returned to Earth for repair. As most of the parts would be designed to fit through hatches used on spacecraft, it might be eventually possible to set up a repair module on either the ISS or a lunar base so that the more simple repairs could be done on site without cycling parts through Earth's gravity well.

If you designed it with expansion in mind, it might even be possible to link different assemblies together or even vehicles to provide more processing power or thrust for bigger jobs without having to design and test a new vehicle.

Items like fuel tanks will probably be too big to go through a standard docking hatch. The spacestation's arm would have to extract the new tank from the side of the cargo vehicle and insert it into the lander. The electrical, mechanical and liquid (pipes) connections would need attaching. A tank could be full or empty.

What goes into an assembly is a decision that involves many trade-offs. Mass, size, cost, reusability and astronaut time. The optimal answer is likely to change with time.

The architecture should be lunar-based meaning that there should be a base on the Moon with a garage that the lander can be brought into and so the lander could be fixed there in a short-sleeved environment. If, however, there was to be a breakdown of a lander in orbit, another, refueled, Moon-based lander would then ascend to the stranded vehicle, attach to it, and bring it back to the lunar surface where it could be repaired within the garage. However, this assumes the presence of a base and crew. Prior to this achievement, reusable landers (i.e. ferries) would be left stranded wherever they are at. Then, after the crew arrives, then the landers could be brought to the garage as I have explained and so the value of the stranded lander would be redeemed as it is repaired.

My personal opinion about how astronauts will refurbish some sort of reusable LEM is that they will use a sort of "space garage" in low moon orbit. The mission would likely go something like this- CSM lifts off, and heads to the moon unencumbered. It than rendezvous with a small station that basically just has a hub, a area for refurbishing the LEM, and a docking port. So anyway, they go to the pressurized area that is essentially a large airlock. They refurbish the LEM unencumbered, and depressurize the airlock and take the LEM down to the lunar surface. They then head up, dock with the station, and head home. Just my two pence.

My personal opinion about how astronauts will refurbish some sort of reusable LEM is that they will use a sort of "space garage" in low moon orbit. The mission would likely go something like this- CSM lifts off, and heads to the moon unencumbered. It than rendezvous with a small station that basically just has a hub, a area for refurbishing the LEM, and a docking port. So anyway, they go to the pressurized area that is essentially a large airlock. They refurbish the LEM unencumbered, and depressurize the airlock and take the LEM down to the lunar surface. They then head up, dock with the station, and head home. Just my two pence.

Propellants are high fire risk and can be poisonousness, so the landers will be kept in vacuum. Reusable landers will have to be designed to permit the replacement of rocket engines and legs using robotic arms. The major components will have to be screwed together rather than welded. Although welding can be used within a component.

Reusable does not have to mean repairable, reusable can instead mean durable. Comsats and space probes last for years on end. The high wear components (engines, landing gear etc.) will be designed for enough cycles to amortize the vehicle. 10 or 25 or 100 landings - whatever makes economic sense.

I'm not an engineer, so I can't come back with detailed descriptions of how different assemblies should be put together. I am imagining that large items like fuel tanks and large portions of the superstructure are going to be unable to be serviced on site and would have to be replaced from Earth. Even in the case of a component that can't be repaired on the Moon, it should be possible to have it removable so that a pre-built section can be swapped out on site. That way, assemblies that can't be repaired on site can be at least be replaced with a spare unit previously shipped up from Earth. The base repair shop can have a 'parts module' with spares ready to be installed in case of failures.

Some items are going to be too dangerous or cumbersome to repair on site, or it won't be cost-effective to ship up specialist equipment to do the repairs. For a lot of the vehicle though (computer subsections, smaller structural parts etc.) then being able to effect repairs on site will greatly speed up the ability to get work done without 'down-time'. Down time in this case will require waiting for stuff from Earth, which will be a huge time and money sink.

If you want to make operations on the moon workable, you are going to have to give them some kind of local autonomy to 'get things done' and that should include as many repairs as can be safely and realistically accomplished.

Remember that Bigelow and Bezos want to be running commercial operations on the Moon eventually. They can't do that if they have to wait a week any time anything fails.

Propellants are high fire risk and can be poisonousness, so the landers will be kept in vacuum. Reusable landers will have to be designed to permit the replacement of rocket engines and legs using robotic arms. The major components will have to be screwed together rather than welded. Although welding can be used within a component.

The fuel would be removed from the lander before the Garage is pressurised.

Propellants are high fire risk and can be poisonousness, so the landers will be kept in vacuum. Reusable landers will have to be designed to permit the replacement of rocket engines and legs using robotic arms. The major components will have to be screwed together rather than welded. Although welding can be used within a component.

The fuel would be removed from the lander before the Garage is pressurised.

The potential for out-gassing would prevent any sharing of air with a habitat. Even inert gas pressurisation (with the maintenance crew wearing breathers) would be inadequate if the lander uses hypergolics for thrusters. It doesn't matter how well you drain the bulk, the traces will (over time) coat the surfaces of the garage; possibly creating a risk of explosion when the contaminated garage-atmosphere is pumped back into tanks when depressurising the garage to open the outer hatch.

Additionally, any pressurisation of a large structure like that will waste a lot of gas, even if you pump the gas back into tanks each time, just due to the sheer size of the "garage".

There might be a way of using a garage module as an unpressurised structure. While the crew still need to do EVAs, the thermal and MMOD environment inside the enclosure would be much more benign. You might be able to come up with an "indoor" suit that has the dexterity of a full EVA suit (or better), but the simplicity of an IVA suit. Likewise, instead of high-maintenance on-suit ECLSS, they could plug into outlets alone the walls that run back into the main station ECLSS; that effectively gives them an unlimited air supply. And because the garage module doesn't need to be pressurised, it can be a vastly simpler and lighter structure, just a frame with soft shielding hung around it, the "hatch" would likewise just be a soft cover. (Even at normal EVA low pressure, you have over 2 tonnes of force per square metre. A hatch big enough to admit a lander would need to be ridiculously strong.)

Even an unpressurised garage still carries the risk of having hypergolics vapour depositing on the walls/suits/airlock/etc, but maybe that's a solvable problem. {shrug}

The walls of the garage/hanger can be designed to allow the astronauts to walk around in gecko boots. Humans find lifting and turning things is easier if the person does not drift away. Mini arms to moving large items may also be useful.

Obviously it would be hard to have a vehicle fully that modular, but conceivably a good serviceable portion could be. Note, ORU's are being robotically serviced now.

Require 80% of the reusable lander to consist of orbital replacement units. Have a design aim of 95% of the units being replaceable. There is always something that is so hard to fix that buying a new vehicle is cheaper - car insurance companies call this a write off.

Require 80% of the reusable lander to consist of orbital replacement units. Have a design aim of 95% of the units being replaceable. There is always something that is so hard to fix that buying a new vehicle is cheaper - car insurance companies call this a write off.

The downside obviously is that it's going to make everything more heavy, and will actually bring down MTBF because of extra complexity in a way of connectors, couplings etc. Probably a price worth paying.

Require 80% of the reusable lander to consist of orbital replacement units. Have a design aim of 95% of the units being replaceable. There is always something that is so hard to fix that buying a new vehicle is cheaper - car insurance companies call this a write off.

The downside obviously is that it's going to make everything more heavy, and will actually bring down MTBF because of extra complexity in a way of connectors, couplings etc. Probably a price worth paying.

When the accountants do the cost trade ensure they include transportation costs. Just moving a large lander from the Earth's surface to the Moon will cost $50 million to $100 million.

Considering the other possibility. Can any of the 'landers' currently flying on Earth perform 10 take-offs and landings without any maintenance?

Can any of the 'landers' currently flying on Earth perform 10 take-offs and landings without any maintenance?

Masten probably could, they did 5 flights in a little over an hour. Being pressure fed, they don't have to worry about pump wear and CSJ engines can last for many thousands of cycles if you design them right. I don't have any inside information on their vehicle maintenance, but I would guess several hundred flights would be possible before needing to replace anything.